If you have no idea of the answer, say you don’t know or you don’t remember or you’d have to think about it. Technical questions are not just posed to see if you know things but also to see how you handle stress. You’ll generally score more points in an interview if you calmly, coolly and matter of factly, state that you don’t the answer than you will fumbling around for ten minutes trying to B/S your way through it. And if you know part of the answer, state the part you know, what you don’t know and move on.